Process for the production of water soluble modified rosin ester vehicles for laminating inks

ABSTRACT

A method for the production of an improved water soluble resin binder for laminating printing inks has been discovered. The method comprises esterifying the carboxylated Diels Alder adduct produced from the reaction of rosin and at least one carboxylated dienophile with a sufficient amount of at least one polyol to produce a modified rosin having an acid number greater than 157. The modified rosin is reacted with a sufficient amount of an acrylic copolymer having an acid number greater than 180 under esterification conditions between 175 ° C. and 185 ° C. for a time sufficient to produce a resin binder having an acid number greater than 157. A laminating ink formulation of the invention comprises water, pigment, styrene-acrylic varnish, shellac varnish, alkanol and the improved water soluble resin binder of the invention as described above.

RELATION TO OTHER PATENT APPLICATIONS

This application is a divisional of the U.S. patent application Ser. No.08/536,014 filed Sep. 29, 1995, now U.S. Pat. No. 5,814,701 which is acontinuation in part of U.S. patent application Ser. No. 08/190,624filed Feb. 2, 1994, now abandoned.

FIELD OF THE INVENTION

This invention relates to a method for preparing superior water-basedresin binders useful in the formulation of laminating inks. The presentinvention particularly relates to a novel method for the production ofstyrenated acrylic modified rosin ester resins useful in laminatingprinting inks. The method of the invention provides rosin ester resinsthat are water soluble and suitable for flexible packaging inkformulation while conferring important improvements in the properties ofthose printing inks.

BACKGROUND OF THE INVENTION

The formulation of printing inks is dominated by the application forwhich the ink is to be used. Inks for gravure printing of paper orpaperboard present a comparatively mild challenge to the artisan toformulate an appropriate ink but other applications can escalate thatchallenge beyond the scope of the state of the art. The requiredpresentation of the printed article, the composition of the substrate onwhich the ink is to be printed and the post-printing process and use towhich the article is to be exposed readily conspire to complicate theformulation process, often creating a need to formulate well beyond thestate of the art. Metallized substrates, food packages and the packingprocess, laminates and the laminating process are just a few examples ofspecific end-uses or post-printing processes offering continuingchallenges to the ink formulation artisan.

Known ink formulations are confronted constantly with the test to meetthe needs of an ever changing mix of consumer products with everchanging print demands. Now, a fundamentally new constraint is beingimposed upon many ink formulations by environmental regulations thaturge a reduction in the use of organic solvents in ink formulations. Forthe more exacting applications such as inks suitable for laminates andthe lamination process, the need to produce water based ink formulationswhich meet or preferably exceed the performance of formulations oflaminating inks known in the art represents a prodigious challenge tothe artisan. To this challenge, the present applicants have bent theirefforts and provided the instant invention of a water based laminatingink formulation with performance properties that exceed those of theprior art.

Inks for lamination comprise a wide range of formulations depending uponthe type of lamination process—adhesive, extrusion lamination orextrusion coating—the many substrates used, adhesive type and end-use ofthe laminate. In the foregoing laminates the printing ink is within theinterface of the two substrates and the performance of the inkformulation must take into account and be compatible with the stressesof the lamination process. Key ink requirements are bond strength to thesubstrate and compatibility with the adhesive. Acrylic-based resins,among others, have been found to be useful as binders in meeting theformulation requirements of laminating inks. The physical mixture ofstyrenated acrylics and rosin esters as binders in flexible packaginginks is known to be particularly useful, but with limitations. Theyusually impart gloss and heat resistance to systems formulated withthem. However, problems such as crinkle resistance, alcohol tolerance,bond strength and rheology can arise with their use.

U.S. Pat. No. 5,164,262 to Boswell, et al. discloses a method for theproduction of an acrylic polymer modified rosin ester binder for gravureprinting ink formulations for paper. The binder is soluble in organicsolvents such as toluene. U.S. Pat. No. 5,166,446 also to Boswell, etal. claims the acrylic polymer modified rosin ester. The Boswell, et al.patent is described hereinafter in greater detail with respect to thepertinency to the instant invention

U.S. Pat. No. 5,026,755 to Kveglis, et al. teaches a water-dispersablegraft copolymer of a polyamide and an acrylic monomer produced by freeradical polymerization.

U.S. Pat. No. 5,183,847 to El-Hefnawi, et al. discloses alkali solubleresins of carboxylated polyamide/acrylic resin prepared by a fusionprocess.

U.S. Pat. No. 5,216,064 to Rivera, et al. teaches rosin-basedresin-fortified emulsion polymer compositions and the method for theirpreparation. The emulsions are prepared by polymerization of vinylmonomers and are used to prepare water based inks.

It is an objective of the present invention to provide a method for theproduction of a water soluble modified rosin-acrylic vehicle forlaminating ink formulation.

Another objective of the invention is to provide a laminating inkexhibiting superior properties and containing the water soluble modifiedrosin-acrylic vehicle.

SUMMARY OF THE INVENTION

Through the application of the discoveries of the present inventionnovel water based laminating inks have been formulated that exhibituniquely superior properties in crinkle resistance, bond strength andalcohol resistance. These achievements have been realized by employingas a vehicle for the laminating inks esterified carboxylated Diels Alderadducts of rosins plus acrylic copolymers. It has been discovered thatwhen these components are reacted under the conditions of the inventiona product of higher molecular weight is produced having a high acidnumber. The product can be used as a vehicle for water based laminatinginks to overcome problems common to the use of conventional laminatingink formulations.

More particularly, a method for the production of an improved watersoluble resin binder for laminating printing inks has been discovered.The method comprises esterifying the carboxylated Diels Alder adductproduced from the reaction of rosin and at least one carboxylateddienophile with a sufficient amount of at least one polyol to produce amodified rosin having an acid number greater than 156. The modifiedrosin is reacted with a sufficient amount of a styrenated acryliccopolymer having an acid number greater than 180 under esterificationconditions between 175° C. and 185° C. for a time from fifteen minutesto forty five minutes to produce a resin binder having an acid numberbetween 157 and 175.

The invention includes a method for the production of an improvedaqueous varnish solution for laminating printing ink comprisingesterifying fumarated gum rosin with a sufficient amount ofpentaerythritol to produce a modified rosin having an acid number of157-175. At a weight ratio of 1 to 1, the modified rosin is reacted withstyrenated acrylic copolymer having an acid number of about 202 underesterification conditions at about 180° C. for about 1 hour whereby aresin is produced having an acid value of 160-173, melting point of155-165° C. and molecular weight of about 14,400. The resin is dissolvedin dilute ammonium hydroxide to provide an aqueous varnish solutionhaving a pH of 8.5 and viscosity of 0.5-2.0 poises.

A laminating ink formulation of the invention comprises water, pigment,styrene-acrylic varnish, shellac varnish, alkanol and the improved watersoluble resin binder of the invention as described above.

DETAILED DESCRIPTION OF THE INVENTION

The use of acrylic copolymers and modified rosin esters as resin bindersin flexible packaging inks has been known for some time. These materialsare the precursors employed in the novel process of the presentinvention to produce the modified resin product whose unique propertiesare responsible for the improved laminating ink formulations describedherein.

The rosins used in the present invention include tall oil rosin, gumrosin and wood rosin. However, gum rosin is the preferred rosin. Theselected rosin is converted to a carboxylated Diels Alder adduct byreaction with a carboxy Diels Alder dienophile under conditions wellknown in the art, preferably between the melting point of the rosin andthe boiling point of the dienophile. The preferred carboxy dienophilesfor reaction with the rosin component are fumaric acid, maleic acid,acrylic acid, methacrylic acid, itaconic acid, citraconic acid andmaleic anhydride.

Upon completion of the Diels Alder reaction, the carboxylated rosinadduct is reacted with a polyfunctional alcohol or polyol and an acryliccopolymer to form a modified rosin ester resin. The polyols orpolyhydric alkanols useful in the invention include pentaerythritol,trimethylolpropane, trimethylolethane, glycerine and the like. Thereaction between rosin adduct and polyol is carried out underesterification conditions, preferably employing basic catalysis. Theratio of esterification reactants and reaction conditions are selectedto produce a polyol esterified adduct having an acid number between 150and 170, but preferably between 157 and 161.

The novel modified resin of the invention is produced by reacting theesterified rosin adduct with an acrylic copolymer. Typical acryliccopolymers include those prepared from acrylic monomers such as acrylicacid, and methacrylic acid plus vinyl monomers such as styrene, alphamethyl styrene, vinyl acetate or mixtures thereof. A preferred copolymeris Joncryl 679®, available from S. C. Johnson, which has an acid numberof 202 and molecular weight of 9,900. The reaction is carried out toproduce a new water soluble higher molecular weight product, i.e., themodified resin product, with an acid number between 157 and 175, butpreferably between 160 and 173.

A key feature of the process of the present invention is the productionof a modified resin having an acid number high enough to confer watersolubility on the product resin and yet advance the ink propertiesprepared from the resin, as described hereinafter. A wide range ofvariables can affect the realization of this objective including theratio of esterified rosin adduct to acrylic copolymer in the reaction,the acid number of the adduct and copolymer, reaction time and reactiontemperature. It has been discovered that a superior resin having an acidnumber between 160 and 173 is produced by reacting the modified rosinand acrylic copolymer at a weight ratio between 1:2 and 1.5:1 when thecopolymer has an acid number of about 180-220, preferably about 202,under esterification conditions at about 175° C. to 185° C. for 15 to 45minutes.

The following example (Example 1) describes a preferred embodiment ofthe present invention leading to the production of a modified rosinester resin that can be used as a vehicle for the preparation oflaminating printing inks with superior bond strength and crinkleresistance. Unless specified otherwise, the term parts in the followingexamples refers to parts by weight.

EXAMPLE 1 Resin Synthesis

100 parts of a pentaerythritol ester of fumarated gum rosin with an acidnumber of 157-161 and melting point of 117-119° C. (manufacturer:Ascona, resin name: FP130) was charged into a 4 neck 1 liter roundbottom flask equipped with a nitrogen blanket, thermometer, mechanicalagitator, and reflux condenser. The contents, when melted, were agitatedmoderately. The temperature was increased and held at 180° C. At thistime 100 parts of a styrenated-acrylic copolymer (S. C. Johnson, Joncryl679 with acid number of 202 and melting point of 146° C.) was added overa ten minute period. Temperature was maintained at 180° C. for one hourand the product was discharged. The resin product had an acid value of160-173; a melting point of 155-165° C.; viscosity of 1-4 poises in a50% ethanol and a weight average molecular weight of 14,400. Gelpermeation chromatographic analysis of the resin showed that a newhigher molecular weight product was formed by the fusion of the tworesins and that the material was not a simple blend of the two startingresins. It was observed that the temperature of the reaction and holdtime were extremely critical. At temperatures above 210° C. the resinwas unstable and a gel formed quickly.

Example 2 describes the method for the preparation of a water basedvarnish using the product from the reaction of Example 1.

EXAMPLE 2 Varnish Preparation

To a 4-neck 1 liter round bottom flask equipped with a nitrogen blanket,thermometer, mechanical agitator, and reflux condenser was charged 275.8parts deionized water and 16 parts ammonium hydroxide. With goodagitation, 108.0 parts of Example 1 was added slowly. The temperature ofthe system was increased and held at 90° C. Upon total solubilization ofthe resin the solution was cooled to 40° C. and discharged. At 27% TNV,and pH of 8.5 the solution viscosity is 0.5-2.0 poises.

A series of experiments, depicted here as Examples 3-8, was carried outto compare the performance of different basic ink formulationscontaining the varnish of Example 2 with a typical basic ink formulationreplacing the varnish of Example 2 with a fumarated rosin.

EXAMPLE 3 Basic Ink Formulations

A. Grinding Portion

Ink Formulation Parts 1. Styrene-Acrylic Varnish (50% (wt.) 24.20 inammonia/water) 2. Water 40.00 3. Defoamer 0.40 4. Phthalocyanine BluePigment 32.00 5. Water 3.40 100.00

The above ink was prepared in the following manner: Initially,ingredients (1-4) were placed in a horizontal mill until the colorantwas properly dispersed. Then item (5) is used to wash out the mill.

B. Letdown portion

Parts 1. Example 2 50.00 2. Shellac Varnish (30%) (wt.) inammonia/water) 28.00 3. n-Propanol 8.00 4. Defoamer 0.50 5. Water 3.40100.00

The above items were added to a high speed mixer and agitated until ahomogeneous vehicle results. The ink was made by adding 55 parts of thegrinding portion to 45 parts of the letdown portion. The vehicles wereagain placed in a high speed mixer for homogeneity. Inks were reduced to12″ on a number 3 Zahn cup with 80/20 (w/w) water: n-Propanol.

EXAMPLE 4

The same ink was prepared as in Example 3 with the exception ofreplacing the varnish of Example 2 in the letdown portion with afumarated rosin.

The properties of the inks prepared in Examples 3 and 4 are compared inTable 1. The Table shows that the properties of the ink prepared withthe resin of the invention (Example 3) has distinctly superiorproperties, particularly with respect to bond strength and crinkleresistance.

TABLE 1 Comparison of Ink Properties with/without New Vehicle PropertyExample 3 Example 4 Flow Newtonian Thixotropic Alcohol Tolerance FluidGels (10% n-PROH) Extrusion Bond 200 g/in 60-100 g/in strength (filmtear) (decal) (commercial polypropylene) Print Quality Smooth lay Severepinholing pH Tolerance 8.0-9.55 9.45-9.55 Crinkle Resistance Very GoodFair

The following Examples 5-6 and 7-8 compare the properties of the resinof the invention with typical formulations containing fumarated rosinresin and employing two different pigments.

EXAMPLE 5

Grinding Portion Parts 1. Styrene-Acrylic Varnish 25.10 (50% (wt.) inammonia/water) 2. Water 40.00 3. Defoamer 0.40 4. AAOT Yellow Pigment32.00 5. Water 2.50 100.00

The above base was prepared according to the procedure set forth inExample 3. The letdown portion was identical to that of Example 3. Theink was prepared in the same manner as that described in Example 3.

EXAMPLE 6

The same ink was prepared as in Example 5 with the exception ofreplacing the varnish of Example 2 in the letdown portion with afumarated rosin resin. Results were comparable to those observed inTable 1.

EXAMPLE 7

Grinding Portion Parts 1. Styrene-Acrylic Varnish 24.90 (50% (wt.) inammonia/water) 2. Water 40.00 3. Defoamer 0.40 4. Barium Red Pigment32.10 5. Water 2.60 100.00

The above base was prepared according to the procedure set forth inExample 3. The letdown portion was identical to that of Example 3. Theink was prepared in the same manner as that described in Example 3.

EXAMPLE 8

The same ink was prepared as in Example 7 with the exception ofreplacing the varnish of Example 2 in the letdown portion with afumarated rosin resin. Results obtained were comparable to thoseobserved in Table 1.

These experiments demonstrate the superiority of the present inventionover those in the prior art. Referring to U.S. Pat. Nos. 5,164,262 and5,116,446 to Boswell, et al., the modified rosin ester products of thatinvention are soluble in aromatic hydrocarbon solvents for use ingravure printing. The high reaction temperatures of those patents arenot useful in the present invention as they cause the resin of theinstant invention to gel. Also, the subject patents produce a product oflow acid number and rely on a much smaller amount of acrylic polymer.The instant invention requires a high acid value of 150-175 for theresin of the invention to be soluble in lower alcohols or amine/watermixtures for aqueous packaging inks.

To define and illustrate the differences between the U.S. Pat. No.5,164,446 of Boswell, et al. and the instant invention a series ofexperiments was carried out as described in the following examples. Theproduct cited by H. Boswell, et al. in “Modified Rosin Esters and TheirUse in Printing Inks”, U.S. Pat. No. 5,164,446, was made according tothe procedure outlined in Examples 1 and 2 of that patent and evaluated.First, as expected, this toluene based vehicle is not water dispersible.Inks prepared utilizing our material in a water based system and theBoswell product in a solvent based system were compared regardingextrusion bond strength, block resistance, printability and tapeadhesion. Example 9 is a summary of this work where A is the Boswell, etal. product and B is the product of the instant invention.

The differences between the process of Boswell, et al. as described inthe preceding paragraph and the process of the instant invention isfurther illustrated by summarizing the process steps of each as follows:

The U.S. Pat. No. 5,164,446 to Boswell, et al.

a) tall oil rosin+fumaric acid are first reacted→rosin adduct;

b) rosin adduct+acrylic-styrene copolymer (Joncryl 587);

c) (b)+CaO are reacted;

d) (c)+glycerine.

The process steps of the instant invention are as follows:

a) gum rosin+fumaric acid→rosin adduct;

b) rosin adduct+pentaerythritol;

c) (b)+acrylic-styrene copolymer (Joncryl 679).

Comparing these process steps it is apparent that the syntheticpreparation of the Boswell, et al. patent differs appreciably from thesynthetic preparation of the instant invention. As further demonstratedherein, the properties of the products of the two processes are uniquelydifferent.

EXAMPLE 9

(Ink A) Boswell, et al. U.S. Pat. No. 5,164,446

Ingredients Parts (Ink A) Boswell, et al. US 5,164,446 PhthalocyanineBlue 17.50 R2450-125 (H. Boswell, et al., EX. #2) 28.00 Toluene 54.50100.00 (Ink B) Invention Hydrobond AX base 55.00 X2-4716 (Ex. of ourinvention) 45.00 100.00 Property (A) Boswell. et al. (B) Invention Watersolubility no yes Rheology Thixotropic Paste Newtonian Fluid ExtrusionBond Strength 0-10 g/in.. 70-100 g/in. (co-extruded, one side treated,polypropylene film) Block Resistance Pass Pass Printability PoorExcelient Tape Adhesion Fair Fair

Comparison of the properties of inks prepared according to the system ofBoswell, et al. with the product of the invention show that the instantinvention is a Newtonian Fluid while the Boswell, et al. material is athixotropic paste. The product of the instant invention has an extrusionbond strength (co-extruded, one side treated, polypropylene film) of70-100 g/in compared to 0-10 g/in for U.S. Pat. Nos. 5,164,262 and5,166,446 to Boswell, et al.

It could be asserted that the distinguishing differences between theBoswell, et al U.S. Pat. No. 5,164,446 is due merely to the fact thatthe Boswell, et al. process uses Joncryl 587, a hydroxy functionalacrylic polyol from S. C. Johnson, in the preparation of their modifiedrosin esters while the instant invention employs Joncryl 679, also fromS..C. Johnson, for the preparation of the water soluble modified resinof the invention. Joncryl 679 is an acrylic copolymer with an acidnumber of 202 and molecular weight of 9,900. Accordingly, a series ofcross-over experiments was carried out substituting for Joncryl 587 astaught in that patent, Examples 1 and 2, the Joncryl 679 employed in theinstant invention. These experiments and their results are presented inExample 10.

EXAMPLE 10

Ingedients Parts (Ink A) Boswell, et al. U.S. Pat. No. 5,166,446Phthalocyanine Blue 17.50 R2621-7 (Boswell patent modified resin exceptusing Joncryl 679 for Joncryl 587) 28.00 Toluene 54.50 100.00 (Ink B)Invention Ingredients Parts Hydrobond AX base 55.00 X2-4716 (modifiedrosin ester of invention) using Joncryl 679. 45.00 100.00 Example 10continued Property Ink (A) Ink (B) Water solubility no yes RheologyViscous fluid Newtonian fluid Extrusion Bond Strength 0 70-100 g/in.(co-extruded, one side treated polypropylene film) Block Resistance FailPass Printability Poor Excellent Tape Adhesion Poor Fair

An additional experiment (Example 11) was carried out to prepare theresin precursor of the Boswell et al. U.S. Pat No. 5,164,446 patentutilizing the Joncryl 587 acrylic styrene polymer.

EXAMPLE 11

The hard resin of Boswell, et al. was prepared according to the processdescribed in Example 1 of the patent (U.S. Pat. No. 5,164,446). Thematerial had an acid value of about 131. It was not soluble in water butwas somewhat soluble in toluene.

In summary, the present invention is distinguished over the prior art bythe following facts:

the invention is a fortified resin for use in formulating laminatinginks, not gravure inks;

the resin of the invention is water soluble, permitting the formulationof water soluble laminating inks;

inks prepared with the resin of the invention are Newtonian fluids, notprior art thixotropic pastes;

bond strength of the invention is very high compared to the prior artand comprise an unexpected result;

printability of inks prepared using the product of the invention isexcellent;

where the prior art fails block resistance and tape adhesion tests, theproduct of the invention passes these critical tests;

the conditions for producing the modified resin of the invention arecritical, specific and different than the prior art, i.e., the reactionis carried out for a period of time between fifteen and forty-fiveminutes at a temperature between 175° C. and 185° C. to produce amodified resin having an acid number between 157 and 175.

What is claimed is:
 1. A laminating ink formulation comprising: water,pigment, styrenated acrylic copolymer varnish and an improved watersoluble resin binder prepared by esterifying a carboxylated Diels Alderadduct produced from the reaction of rosin and at least one carboxylateddienophile with a sufficient amount of at least one polyol to produce amodified rosin having an acid number greater than 150; and reacting saidmodified rosin in a 1:1 weight ratio with a styrenated acrylic copolymerhaving an acid number greater than 180 under esterification conditionsbetween 175° C. and 185° C. for a time between 15 and 45 minutes toproduce said water soluble resin binder having an acid number between157 and 175.